The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets
Andrej Classen,
Christos L. Chochos,
Larry Lüer (),
Vasilis G. Gregoriou,
Jonas Wortmann,
Andres Osvet,
Karen Forberich,
Iain McCulloch,
Thomas Heumüller () and
Christoph J. Brabec ()
Additional contact information
Andrej Classen: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Christos L. Chochos: Advent Technologies SA
Larry Lüer: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Vasilis G. Gregoriou: Advent Technologies SA
Jonas Wortmann: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Andres Osvet: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Karen Forberich: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Iain McCulloch: University of Oxford
Thomas Heumüller: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Christoph J. Brabec: Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander University Erlangen-Nürnberg
Nature Energy, 2020, vol. 5, issue 9, 711-719
Abstract:
Abstract Organic solar cells utilize an energy-level offset to generate free charge carriers. Although a very small energy-level offset increases the open-circuit voltage, it remains unclear how exactly charge generation is affected. Here we investigate organic solar cell blends with highest occupied molecular orbital energy-level offsets (∆EHOMO) between the donor and acceptor that range from 0 to 300 meV. We demonstrate that exciton quenching at a negligible ∆EHOMO takes place on timescales that approach the exciton lifetime of the pristine materials, which drastically limits the external quantum efficiency. We quantitatively describe this finding via the Boltzmann stationary-state equilibrium between charge-transfer states and excitons and further reveal a long exciton lifetime to be decisive in maintaining an efficient charge generation at a negligible ∆EHOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at a very small ∆EHOMO. Ultimately, highly luminescent near-infrared emitters with very long exciton lifetimes are suggested to enable highly efficient organic solar cells.
Date: 2020
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Persistent link: https://EconPapers.repec.org/RePEc:nat:natene:v:5:y:2020:i:9:d:10.1038_s41560-020-00684-7
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DOI: 10.1038/s41560-020-00684-7
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